In many procedural languages (such as python), I can "unpack" a list and use it as arguments for a function. For example...
def print_sum(a, b, c):
sum = a + b + c
print("The sum is %d" % sum)
print_sum(*[5, 2, 1])
This code will print: "The sum is 8
"
Here is the documentation for this language feature.
Is there a way to replicate this argument-unpacking behaviour in Prolog?
For example, I'd like to unpack a list variable before passing it into call.
Could I write a predicate like this?
assert_true(Predicate, with_args([Input])) :-
call(Predicate, Input).
% Where `Input` is somehow unpacked before being passed into `call`.
...That I could then query with
?- assert_true(reverse, with_args([ [1, 2, 3], [3, 2, 1] ])).
% Should be true, currently fails.
?- assert_true(succ, with_args([ 2, 3 ]).
% Should be true, currently fails.
?- assert_true(succ, with_args([ 2, 4 ]).
% Should be false, currently fails.
You may think that this is an XY Problem. It could be, but don't get discouraged. It'd be ideal to receive an answer for just my question title.
You may tell me that I'm approaching the problem poorly. I know your intentions are good, but this kind of advice won't help to answer the question. Please refer to the above point.
Perhaps I'm approaching Prolog in too much of a procedural mindset. If this is the case, then what mindset would help me to solve the problem?
I'm using SWI-Prolog.
The built-in (=..)/2
(univ) serves this purpose. E.g.
?- G =.. [g, 1, 2, 3].
G = g(1,2,3).
?- g(1,2,3) =.. Xs.
Xs = [g,1,2,3].
However, note that many uses of (=..)/2
where the number of arguments is fixed can be replaced by call/2
...call/8
.
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